Birdwatchers are growing increasingly concerned that the unhatched fourth peregrine egg could be ditched by the female.
The pair’s third egg hatched on Monday in their rooftop nest at the top of Chichester Cathedral.
But after several days without any sign of movement from the fourth and final egg, RSPB experts fear it may not hatch at all - and could be left aside.
“As all who are watching the live feed and counting the days since the third chick hatched, we are possibly looking at a failed egg,” wrote RSPB staff on their Facebook page.
“This is more common than we have grown to expect but it is natural to have some failures. To date we have had six failures over the 13 years, the initial four in the very first year (possibly due to immaturity), and two (in two different seasons) since that time.”
If the egg doesn’t hatched, it will be edged out of the way - so all eyes are on the nest in the skies for now, they added.
“An egg which fails will be pushed aside by the female (and our ever-growing chicks) and it will usually end up at the side or far enough away it will not be disturbed by the activities on the scrape.
“While we still have hope, we will also keep a watch out for this activity to start, which will be our confirmation it has failed.”